Anal Furunculosis

Canine anal furunculosis, also called perianal fistula, is a formation of an abnormal channel (fistula) between the anal canal and the skin surrounding the anus. The continual discharge of watery pus from the fistula can irritate the skin and result in itching, discomfort and pain. Most anal fistulas are caused by abscesses that spread from inside of the anus to the outer surface of the skin. The disease is most common in the German Shepherd Dog and Irish Setter breeds, and occasionally in other breeds. Males outnumber females by 2 to 1. Dogs older 7 years are at higher risk. Deep anal folds may cause feces to be retained within rectal glands and play a significant role.

The definitive causes this condition have not been determined. Researches have explored many factors, including overproduction by local secretory glands, poor ventilation associated with low tail carriage, anal sac disease, hip dysplasia, and inflammatory bowel disease. Low thyroid hormone levels and an immune system defect may also contribute to susceptibility. The current theory involves a multifactorial immune-mediated disease process which is suspected because both canine anal furunculosis and Crohn's disease respond to therapy targeted at the immune system. Accumulating evidence shows that Crohn's disease is the result of an unbalanced host immune response to intestinal triggers in genetically susceptible humans. Because German Shepherd Dogs with anal furunculosis also have clinical and histological evidence of inflammatory bowel disease, it is possible that dietary antigens, bacterial antigens, and superantigens may be initiators as well.

Clinical signs vary. There may be multiple draining tracts and ulcers immediately surrounding the rectum. Animals may present pain and spasm when attempting to evacuate the bowels (tenesmus), difficulty in defecation, and constipation. Affected area is usually very painful. Other signs seen in this condition consist of passage of red blood through the rectum; constipation; diarrhea; ribbon-like stool; increased frequency of defecation; perianal pus-filled discharge or bleeding; perianal licking; self mutilation; scooting;
offensive odor; low tail carriage; and weight loss.

Diagnosis is based on history, physical findings and skin biopsy. Culture and sensitivity tests are performed, if antibiotic therapy is being considered as part of the treatment. The most common organisms recovered from culture include: E. coli, Staphylococcus aureus, beta-hemolytic Streptococcus, and Proteus mirabilis. Keep in mind that antibiotic therapy has very little impact on the clinical outcome. Management of these cases is often disappointing because they do not respond consistently to antibiotics, corticosteroids and surgery. Keep the affected area clean by clipping the hair and flushing the lesions with chlorhexidine or povidone iodine. Post-operative complications include recurrence of fistulas, fecal incontinence, tenesmus, and difficulty in defecation. The carbon dioxide laser has been an effective adjunctive tool in treating canine anal furunculosis in some dermatology practices.

It is important for owners to understand that canine anal furunculosis is a chronic relapsing and remitting disease that can be managed but not necessarily cured. Lifelong therapy may be required as with other immune-mediated diseases. The first goal of therapy is to alleviate tenesmus, blood discharge from the rectum, constipation or obstipation, diarrhea, ribbon-like stool, increased frequency of defecation, and perianal pain. The second goal of therapy is to reduce the diameter, depth, extent, and recurrence of sinus tracts. It is important to keep the perianal region clean and dry. Baby powder may reduce humidity. At home, antimicrobial shampoo therapy may be helpful once the patient will tolerate it.